The disclosure relates generally to improvements in petroleum recovery and gas recovery processes in the field.
Liquid carbon dioxide (CO2) is an attractive fluid for many hydraulic fracturing applications because it contains no water (i.e., it is “dry”) and therefore does not damage water-sensitive sandstone or shale formations. The use of pure or substantially high loadings of CO2 in fracking for petroleum and gas recovery is affected by the low viscosity of CO2 which reduces the fracture size and does not allow for effective proppant suspension and delivery to the fracture sites. Thus pure CO2 remains an ineffective dry fracking fluid because the low viscosity of liquid CO2 does not permit effective fracturing of the rock strata to generate the fissures needed for efficient petroleum or gas extraction
In some known methods, liquid CO2 has been combined with an aqueous surfactant solution to generate CO2-in-water (i.e. bubbles of liquid CO2 inside of thin films of surfactant-stabilized water) emulsions or foams for hydraulic fracturing that have a high apparent viscosity. The aqueous phase has included a water-soluble alcohol. However, the presence of water in these previously described CO2-in-water foams renders them “wet”.
A dry emulsion or foam can be composed of bubbles of high pressure liquid separated by films of surfactant-stabilized oil if the CO2 and oil are not miscible. Although conventional surfactants with hydrophobic and hydrophilic segments have been used to form stabilized CO2 emulsions or foams which are injected into the well bore, the foam strength varies depending on the surfactant used. R.E. Greenhorn and E. Li Petroleum Society of Canada, Paper Number-85-36-34, Annual Technical Meeting, Jun. 2-5, 1985, Edmonton, Alberta; G. W. Lancaster et al., Petroleum Society of Canada Paper Number 87-38-71, Annual Technical Meeting, Jun. 7-10, 1987, Calgary, Alberta. There is an ongoing need in the field for design and optimization of chemical structure and compositions of CO2 foaming agents under realistic reservoir temperature and pressure conditions.